The broad aim of this research project is to contribute to the further understanding of the development and utilization of inferred mediational processes of young children. A principal objective is to test certain assumptions generated by the proposed mediational model in both reversal-extradimensional shift and optional shift studies. The model incorporates, among others, theoretical notions proposed by Piaget and the Kendlers. The basic assumptions that serve as the model's foundation is that although the young child may begin life responding in an S-R linkage manner, he soon, perhaps by the time he reaches the age of three, begins to develop the ability to use motor-imagery as a mediational device. It is during the child's first few years of school that he first begins to use verbal mediators. It is therefore postulated that the 3-5 year old child is able to use mediational type processes which are different in mode from those used by schoolage children. The model not only has implications for our understanding of the preschool age child's learning and memory capacities but may also suggest ways in which we might facilitate learning and memory of the mentally retarded. Another objective is to continue the exploration of the relationship between child's development of concepts and the formation of stimulus organization in adult humans.